This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The long term goal of this research is to understand the mechanisms by which cells respond to DNA damage. The link between DNA damage and human health is well-established: the inability to correctly repair damaged DNA can result in various forms of colon, breast, and ovarian cancers in humans. The existence of similar, extensive DNA damage sensing and repair mechanisms in organisms ranging from humans to bacteria demonstrates this central role of DNA integrity. In the typical bacterial SOS response pathway, after DNA damage, the UmuD protein self-cleaves, and then acts with its partner, UmuC, to function as a translesion synthesis DNA polymerase.